This invention relates to electrostatic-discharge protective materials, and more particularly to such materials as used for the packaging of electronic components, and bags of such material,
During recent years, the increasingly frequent shipments of electrostatic-sensitive electronic components have necessitated the development of packaging materials that protect the components from electric shocks and discharges. It is particularly desirable that these materials have the flexibility to be folded over and sealed along the sides to form an inexpensive bag or envelope within which to hold the electronic components. Moreover, it is desirable that the material be transparent enough to identify visually the component through the material. Accordingly, various flexible sheet materials have been developed for such use. Typically, as shown in U.S. Pat. Nos. 3,801,418 (Cornelis et al.), 4,407,872 (Horii), and 4,424,900 (Petcavich), these materials are in the form of a sheet comprising a conductive metal layer. In at least one case, U.S. Pat. No. 4,529,087 (Neal et al.), a sheet material without a metal layer is shown imprinted with a conductive ink.
However, while these materials may afford an electronic component some electrostatic discharge protection, they suffer serious drawbacks. When such flexible sheet materials having a metal layer are creased, resulting either from the folding of the material to form a bag or envelope for receiving an electronic component or from accidental damage, the metal layer tends to crack, disrupting conductivity. Thus, the protective quality of the material is reduced.
On the other hand, a conductive ink layer, particularly one that is flexible enough to adapt to such folding or creasing, does not provide sufficient conductivity to produce the degree of electrostatic charge dissipation desired to protect sensitive electronic components.
Therefore, flexible sheet material and bags or envelopes made therefrom are still needed that will adequately protect electronic components, even after the material is folded or creased.